Assembly of nanoelements on a template with precise alignment and orientation followed by transfer of the nanoelements to a recipient substrate is expected to accelerate large-scale production of nanoscale devices. However, absence of highly versatile and reusable templates for high-throughput directed assembly and transfer with minimal deterioration have hindered any progress.
Various templates fabricated through bottom-up or top-down processes have been used to assemble nanoelements for achieving desired architectures [1-3]. The template-guided fluidic assembly process is amenable to a variety of nanoelements and can result in high assembly density, yield and uniformity [4-6]. However, the assembly process is very slow and hence not scalable. On the other hand, electrophoretic assembly involves assembling nanomaterials having a surface charge on a conductive surface over large areas (wafer scale) in a short period of time [7-10]. When nanoelements are assembled by electrophoresis on a topographically patterned electrode with interconnected microscale and nanoscale features, due to the differences in potential drop at various regions of the electrode, the assembly is non-uniform. Previously, this impediment has been circumvented by employing so-called “trench templates” in which a lithographically-defined polymer pattern lies on top of a uniform conducting layer guiding the assembly to the desired locations. Whenever assembled nanoelements in these trench templates needed to be transferred to a recipient substrate, the polymer has to be removed, thereby limiting the template's use to a single assembly and transfer cycle [11].
Transferring assembled nanoelements from one substrate to another while retaining their two-dimensional order is a rather cumbersome process requiring in-depth knowledge about the interaction energy between different materials and the nanoelements. Successful achievement of ordered nanoelement transfer onto flexible substrates would enable the production of various types of new devices such as thin-film transistors, gas sensors, and biosensors [12-14]. Even though transfer of nanoelements using a template sacrificial layer (e.g. SiO2 layer) has been demonstrated for transfer onto flexible as well as rigid substrates, and with high transfer efficiency, such templates cannot be reused [15]. Intermediate sacrificial films such as PDMS and Revalpha thermal tape for transferring nanoelements to the recipient substrates have also been explored, but these introduce additional steps and hence result in a complicated fabrication process leading to higher production costs [16-17].